The long range objective of the project is to broadly advance biomedical research by improving the performance of bonded phase substrates in the high performance liquid chromatographic (HPLC) separation of basic drugs inbiological fluids. Determinations of pharmaceuticals by HPLC is currently limited by undesirable and irreproducible partitioning between the organic base and acidic silanol sites on the surface of siliceous alkylmodified supports in HPLC columns. The specific aims of the research are three-fold. The first aim is to study and optimize experimental factors of the alkylsilylation reaction with silica, to yield surfaces with maximum silane laoding, minimal number of accessible and acidic silanol sites, and reproducible composition. The second aim of the research is to study the kinetics of the silylation reaction insolution and gaseous phases. Results of these studies will contribute to a better understanding of the modification process and the development of innovative strategies to affect a more efficient bonded phase substrate. The third aim is to assess the HPLC performance of alkylsilylated silicas in separations of basic drug mixtures. The surface composition of alkylmodified silicas will be characterized through the acquisition and interpretation of diffuse reflectance FTIR spectra (DRIFTS). Infrared absorption bands indicative of unreacted silanol sites (3743 cm-1) and the attached alkyl reagent (2900 cm-1) will be used to assess the extent of the silylation reaction. Absolute silane surface coverage will be quantified by obtaining total weight percentage carbon data from which silane concentration (mumol/m2) will be calculated. Modified silicas will be packed into stainless steel columns and a series of test mixtures of basic pharmaceuticals will be analyzed using the columns under a standard set of operating conditions. Chromatographic parameters of selectivity factor (alpha), peak asymmetry (A), capacity factor (k'), theoretical plates (N) and column stability will be assessed, and correlated to surface structure of bonded phase packing materials.